A Thermodynamic Study of Pressure Gain Combustion in Combined Cycles

Abstract

Listen

Translate article

Abstract Gas turbines are internal combustion engines based on the Brayton-Joule cycle with four thermodynamic processes including air compression, constant pressure combustion, gas expansion and heat rejection. Actually, a relevant increase in entropy production is related to the constant pressure combustion, even in the ideal cycle, so alternative combustion solutions, such as the Pressure Gain Combustion (PGC), are worthy of attention. This work aims at investigating PGC potential in gas turbines compared to conventional power plants based on the Brayton-Joule cycle. Both simple cycle and combined cycle operations are considered, focusing on a F-class gas turbine unit for power production. Cycle performance is estimated through a thermodynamic in-house code, where the common calculation scheme has been revised in order to simulate a combustion process occurring with increasing pressure from inlet to outlet of the combustor. A booster compressor is necessarily included in the power system for delivering the cooling air to the first stage blades of the turbine. The results are fully satisfactory as PGC technology really improves the efficiency of the gas turbine expander: in case of a pressure gain of 45%, which is a reasonable value based on literature data, 1.3 to 3.4 percentage points more in gas turbine efficiency have been calculated. Finally, a parametric analysis of expansion efficiency penalties due to supersonic pulsating flows at the first stage of the turbine expander is presented.